Control systems for various apparatuses rely on a plurality of switches to input data to the apparatus. Switch arrays based on mechanical switches mounted on a surface are well known in this regard. Simulated switch arrays that utilize touch screens are also well known. Mechanical switch panels are difficult to reconfigure, and hence, tend to be customized for each application. This substantially increases the cost and product cycle time of devices that utilize such panels.
Input devices based on touch screens provide a convenient method for inputting commands in a manner that is easily reconfigurable. In such devices, the button pattern is displayed on the screen and the user selects a “button” by touching the screen over the button image. Touch screens, however, are significantly more expensive than conventional switches, and hence, are not always feasible for many applications. In addition, the ambient light intensity can interfere with the display that prevents the user from seeing the simulated buttons. Furthermore, the device cannot distinguish between an accidental light touch and an intended button push, since the screens do not provide a measure of the pressure with which the user has pressed his or her finger on the screen.
Many touch screen designs depend on detecting a change in some electrical parameter such as resistivity or capacitance that varies with the location on the screen at which the user touches the screen. Since the observed changes depend on the shape of the screen, custom screen sizes are limited and can require special programming.
Generic switch panels that overcome or that significantly reduce these problems are disclosed in co-pending U.S. patent application Ser. No. 10/810,157 filed Mar. 25, 2004 and Ser. No. 11/215,180 filed Aug. 29, 2005, which are hereby incorporated by reference. In those systems, a switch panel is constructed from a touch plate, image generator, and imaging system. The touch plate includes an optically transparent layer having first and second sides. The optically transparent layer has an index of refraction greater than that of air. A light source generates a light signal that is reflected between the first and second sides of the touch plate within the transparent layer. The imaging system records an image of the first surface of the touch plate. When a user presses a finger on the touch plate, a portion of the internally reflected light is reflected toward the second surface at an angle greater than the critical angle and the light escapes the second surface. The location of the bright spot created on that surface is recorded by the imaging system. A simulated button push is then generated based on the location of the detected bright spot.
While this type of system represents a significant improvement over prior art systems, there are still areas that could be improved. First, many users would prefer systems that provide feedback when the system recognizes a “button” as being pushed. While the system taught in this disclosure can provide that feedback by utilizing a sound generated by the controller when a touch is recorded, this requires additional programming and depends on some additional hardware being present with the touch screen, i.e., some form of sound generating apparatus.
Second, the system requires an imaging system that views the touch screen. Imaging systems require optics and a significant amount of space. The entire active area of the screen must be imaged on the imaging array. Hence, there must be a substantial distance from the screen to the imaging array. This increases the thickness of the display. In addition, the various optical components must be mounted and aligned, which increases the cost of the display. Finally, non-planar switch panels impose serious limitations on the optics, since the non-planar surface must be imaged onto the imaging array.